[PATCH] vfio-ccw: Do not read region ret_code after write

[Eric Farman]

A pwrite() call returns the number of bytes written (or -1 on error),
and vfio-ccw compares this number with the size of the region to
determine if an error had occurred or not. If they are equal, the
code reads the ret_code field from the region. However, while the
kernel sets the ret_code field as necessary, the region and thus
this field is not "written back" to the user. So the value can only
be what it was initialized to, which is zero.

Not harming anything, but it's a puzzle. Let's avoid the confusion
and just set the return code to zero for this case.

Suggested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 hw/vfio/ccw.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
index bc78a0ad76..bfd5fd07a5 100644
--- a/hw/vfio/ccw.c
+++ b/hw/vfio/ccw.c
@@ -106,7 +106,7 @@ again:
         error_report("vfio-ccw: write I/O region failed with errno=%d", errno);
         ret = -errno;
     } else {
-        ret = region->ret_code;
+        ret = 0;
     }
     switch (ret) {
     case 0:
@@ -194,7 +194,7 @@ again:
         error_report("vfio-ccw: write cmd region failed with errno=%d", errno);
         ret = -errno;
     } else {
-        ret = region->ret_code;
+        ret = 0;
     }
     switch (ret) {
     case 0:
@@ -234,7 +234,7 @@ again:
         error_report("vfio-ccw: write cmd region failed with errno=%d", errno);
         ret = -errno;
     } else {
-        ret = region->ret_code;
+        ret = 0;
     }
     switch (ret) {
     case 0:
-- 
2.25.1